Two days later he tweeted a picture of himself with International Trade Secretary Liam Fox “discussing our trade agreements post Brexit”.

The UK’s House of Commons Code of Conduct states that MPs must declare any visit to a destination outside the UK which “relates in any way to their membership of the House or to their parliamentary or political activities” and which cost more than £300, unless they have paid for it themselves or out of parliamentary or party funds.

The rules state the British MPs do not have to register family holidays, so long as they are “wholly unconnected with membership of the House or with the member’s parliamentary or political activities”.

Entries in the Register of Members’ Interests should cover the cost of travel, hotels, meals, hospitality and car hire, and repeat visits should be registered if their combined value comes to over £300.

Mr Paisley’s Register entries include a trade mission to Sri Lanka in 2012, as well as a second trip to the island that year as part of a cross-party parliamentary delegation examining post-war reconstruction, funded to the tune of £3,200 by the Colombo government.

There is no mention of the alleged trips in 2013.

Complaints over alleged breaches of the Code are investigated by the Parliamentary Standards Commissioner Kathryn Hudson, who reports to the Commons Standards Committee.

This committee, made up of MPs and lay members, has the power to recommend sanctions such as requiring an apology or temporary suspension, subject to a vote in the Commons.